Fiber Cement Siding in St. Louis

What the code asks of fiber cement

The residential code treats fiber cement as its own material. Under IRC section R703.10, lap siding up to 12 inches wide has to comply with ASTM C1186 as Type A, at least Grade II. Table R703.3(1) sets a minimum thickness of 5/16 inch for both lap and panel siding. For lap siding the code also requires:

• a lap of at least 1-1/4 inches between courses;
• protected butt joints, using caulk, an H-shaped joint cover, or a strip of flashing behind the joint;
• fastening by the table or the maker's approved instructions, face-nailed or blind-nailed through the top edge with a galvanized roofing nail at each stud.

Panels get their own rule: vertical and horizontal joints fall over framing and are caulked, battened, flashed or shiplapped.

One number people do not expect: James Hardie's code evaluation report lists a 5/16-inch plank at about R-0.15. Fiber cement keeps water and fire off the wall. It does nothing for insulation.

Lap, shingle and panel profiles

Most fiber cement on houses here is lap siding, the horizontal clapboard look. James Hardie's evaluation report lists its standard planks at 5/16 inch thick, in widths from 4 to 12 inches, with smooth or wood-grain faces. A thicker 5/8-inch lap line is made for a deeper shadow line.

Shingles come as individual pieces or as four-foot panels with square, staggered or half-round bottom edges, 1/4 inch thick. Large vertical panels with battens give a board-and-batten look, and the code covers them under its panel siding rule.

Lap planks are not trim. The installation instructions rule out using them as fascia or trim, so corners, windows and the roof edge get trim boards in fiber cement or cellular PVC, which is also what the Cost vs. Value project assumes.

Some suburbs care about the look. Kirkwood's architectural guidelines put clapboard of wood or fiber cement among the preferred materials, and ask that it imitate the profile of traditional wood siding, so the plank you pick matters there.

Factory finish or field paint

You can buy fiber cement two ways: primed, for painting on site, or with a finish applied at the factory. The Cost vs. Value project assumes the factory finish.

Primed and field-painted. James Hardie's instructions say factory-primed product must be painted within 180 days of installation. They recommend 100% acrylic topcoats, rule out stain, oil or alkyd paint and powder coating, say not to paint when the siding is wet, and recommend back-rolling if the paint is sprayed. The upside is any color you want and a finish you can control.

Factory-finished. The color arrives on the board, so the house is finished when the last plank goes up. It changes the details: the maker recommends joint flashing rather than caulk at butt joints, because caulk and factory finish weather differently, says not to caulk nail heads, and requires its own touch-up and edge-coating products where boards are cut.

Installation rules that decide the warranty

The maker's instructions warn that not following them may affect building envelope performance and warranty coverage. The ones that matter most:

• Clearances. 6 inches above the ground; 2 inches above a roof, deck, path, step or slab; 1 inch from the end of a gutter; and 1/4 inch above horizontal Z-flashing, with that gap left uncaulked so water can get out.
• Butt joints. Planks meet in moderate contact, over joint flashing or another code-approved joint treatment.
• Nailing. Blind nailing is the preferred method, 3/4 to 1 inch below the top edge and 3/8 inch from the ends, with at least 1-1/4 inches of lap. Face nailing is for high-wind requirements and is never mixed with blind nailing on the same plank.
• Nail depth. Heads snug to the surface, not sunk. A pneumatic nailer with a flush-mount attachment helps; overdriven nails need correcting.
• Cut edges. Every field-cut edge is caulked, primed or painted.
• Storage. Planks stored flat, dry and covered. Installing them wet can open gaps at the butt joints as they shrink.
• A flat wall. Irregular framing and sheathing show through the finished siding, so they get corrected first.

Silica dust: how it should be cut

Fiber cement contains respirable crystalline silica, and breathing too much of it can cause silicosis, a disabling lung disease. OSHA's construction silica standard, 29 CFR 1926.1153, limits a worker's exposure to 50 micrograms per cubic meter averaged over eight hours. For handheld saws cutting fiber-cement board with a blade of 8 inches or less, the standard's Table 1 lays out a method: cut outdoors only, with a saw fitted with a commercially available dust collection system, maintained to the tool maker's instructions, with the airflow the maker recommends and a filter that is 99% efficient or better. Follow that and no respirator is required for the task.

James Hardie's instructions add the site rules: set the cutting station where the airflow carries dust away from people, prefer a vacuum-connected saw or shears, never use a power saw indoors, and clean up with a vacuum or wet methods instead of dry sweeping.

What that means for you: ask where the cutting station will be, what saw will be used, and how the dust is cleaned up. If the saw has no dust collection, ask how the crew is keeping under the OSHA limit, and keep windows near the cutting station closed.

Weight, walls and handling

James Hardie's specification sheet puts its standard lap siding at 2.31 pounds per square foot. At that rate the 1,250 square feet in the Cost vs. Value project comes to roughly 2,900 pounds of board on the walls, and every pound is lifted, cut and held in place by hand.

The weight changes the job in three ways. Planks have to be carried on edge and handled with care, because the corners and edges break, and the instructions for planks with a formed drip edge ask for extra care so that edge is not damaged. The wall underneath must be sound: the maker allows studs up to 24 inches apart or direct nailing to OSB at least 7/16 inch thick. And it costs more to put up than vinyl, as the regional figures below show.

On an older house with wavy walls, expect time spent shimming and straightening before the first plank goes on. Fiber cement is rigid, and it will show every bump it is nailed over.

Fiber cement and St. Louis rules

Two quirks of local permitting land on fiber cement in particular. The City of St. Louis lists aluminum, steel and vinyl siding as permit-free when no opening changes, and says nothing about fiber cement. University City exempts only prefinished metal or vinyl installed over existing walls. In both places, plan on asking for a permit for a fiber-cement re-side. Unincorporated St. Louis County, by contrast, exempts re-siding in any material. Every jurisdiction's rule is on our permits page.

Climate matters for which product you buy. The County's design table, part of the residential code it adopted, shows a 30-inch frost line and rates weathering as severe. James Hardie sells climate-zoned versions of its planks, and its instructions tell installers to confirm the right zone product for the address before installing. Ask which one your quote is for.

Historic districts can rule it out entirely: Shaw's standards bar siding of any type. See historic districts.

Cost: why it earns back 103.3% here

For the West North Central census division, which includes Missouri, Zonda's 2025 Cost vs. Value Report prices a fiber-cement re-side at $23,470 and its added resale value at $24,236, so 103.3% of the cost comes back. Nationally the same job is $21,485 and 113.7%. The defined project takes off 1,250 square feet of old siding and puts up fiber cement that is primed and painted at the factory, trimmed throughout with 4/4 and 5/4 boards of fiber cement or cellular PVC, over a continuous water-resistive barrier.

Against the vinyl project in the same report, the fiber-cement job costs about $4,560 more here, and the real estate agents surveyed valued it about $8,870 higher at resale. That is a survey of opinion, not a promise about your house, but it is the one siding row in the regional table that comes out ahead.

Your own number moves with factory finish versus primed and painted, trim choices, wall height and openings, how much straightening the walls need, rot found under the old siding, and lead-safe work on a pre-1978 house. See siding replacement for the whole job.

Common questions about fiber cement siding in St. Louis

Where we work

Fiber cement siding across greater St. Louis, from the city and St. Louis County out to St. Charles, Jefferson and Franklin Counties and across the river into the Metro East. Each city has its own page with the permit rule and code edition that apply there: